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CHAPTER 4 ATM CELL PROCESSOR
Preliminary User’s Manual S14767EJ1V0UM00
337
Figure 4-47. Rate Field ABR Parameter
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4.8.5.4 ABR service operation
(1) Sets registers for ABR service
(2) Open_Channel
In ABR service, since ATM Cell Processor uses both Tx VC table and Rx VC table, V
R
4120A RISC Processor
has to open two channel. In ABR service, although ATM Cell Processor only transmits data and not receives
any data, receiving VC is required to receive BRM cell. The other way, although ATM Cell Processor only
receives data, transmitting VC is required to transmit FRM cell.
(3) Setting VC tables
As described above, in ABR service, both transmit and receive channels are always used together. So that,
both transmit and receive VC tables have to be set before transmitting ABR cells or receiving ABR cells. There
are special parameters for ABR service. Most of these parameters are obtained from connection negotiation.
(4) Setting Receive lookup table
In ABR service, although ATM Cell Processor only transmits cells and not receives, it has to receive BRM cells.
If ATM Cell Processor only receives BRM cells and not receives any data cells, V
R
4120A RISC Processor
doesn’t have to reserve receiving pool, but if ATM Cell Processor receives data cells, V
R
4120A RISC
Processor has to reserve receiving pool.
(5) Tx_Ready command
The operation for this command is as same as the ones for other service classes.
(6) Transmit and Receive indications
The operation for this command is as same as the ones for other service classes.
(7) Close_Channel
In ABR service, both transmit and receive channels have to be closed at a time. V
R
4120A RISC Processor has
to close transmit channel first and then receive channel.
4.8.5.5 RM cell operation
ATM Cell Processor manages RM cells internally. V
R
4120A RISC Processor doesn’t have to do anything on RM
cells. ATM Cell Processor manages RM cells according to source/destination behavior.
RM cell operation at the source side
Transmit FRM cells periodically. ATM Cell Processor also transmit out-of-rate FRM cells with TCR. If ATM Cell
Processor receives BRM cell, it recalculate ACR value using information in BRM cell. V
R
4120A RISC
Processor doesn’t have to reserve FRM cell data in transmit buffer in SDRAM.
RM cell operation at the destination side
When ATM Cell Processor receives FRM cell, it automatically send back BRM cell. ATM Cell Processor follows
destination behavior to send back BRM cell. Received FRM cell is not stored in receiving pool in SDRAM. ATM Cell
Processor processes it internally.